refactor: fix representation according to general standard

Author: alxkm

src/main/java/com/thealgorithms/conversions/DecimalToHexadecimal.java

@@ -24,6 +24,19 @@ public static String decToHex(int decimal) {
             hexBuilder.insert(0, HEX_DIGITS[currentHalfByte]);
             decimal >>= NUMBER_OF_BITS_IN_HALF_BYTE;
         }
-        return hexBuilder.toString().toLowerCase();
+        return removeLeadingZeros(hexBuilder.toString().toLowerCase());
+    }
+
+    private static String removeLeadingZeros(String str) {
+        if (str == null || str.isEmpty()) {
+            return str;
+        }
+
+        int i = 0;
+        while (i < str.length() && str.charAt(i) == '0') {
+            i++;
+        }
+
+        return i == str.length() ? "0" : str.substring(i);
     }
 }

src/test/java/com/thealgorithms/conversions/DecimalToHexadecimalTest.java

@@ -7,7 +7,7 @@
 
 public class DecimalToHexadecimalTest {
     @ParameterizedTest
-    @CsvSource({"0, 00000000", "1, 00000001", "10, 0000000a", "15, 0000000f", "16, 00000010", "255, 000000ff", "190, 000000be", "1800, 00000708"})
+    @CsvSource({"0, 0", "1, 1", "10, a", "15, f", "16, 10", "255, ff", "190, be", "1800, 708"})
     void testDecToHex(int decimal, String expectedHex) {
         assertEquals(expectedHex, DecimalToHexadecimal.decToHex(decimal));
     }